Stripping and recoating of aircraft is a routine practice in the aerospace industry. In this process, redundant layers of paint are stripped away either chemically and/or mechanically to minimize the weight build-up before a fresh layer is applied. The use of an intermediate coating (IC) layer based on solutions of synthetic resins in organic solvents, applied for example between the topcoat and primer is known for facilitating ‘selective’ stripping of the topcoat without affecting the integrity of the underlying primer or substrate. Such a strategy has benefits in terms of flow time reduction to complete the re-coating process and protection of the underlying materials from the stripper medium.
The use of barrier coatings composed of modified epoxy-polysiloxanes or film-forming polymers applied between the substrate and top coat have also been described. The barrier coating technique focuses on improving the chemical resistance of the primer and aims to reduce the capacity of the stripping solution to degrade the primer and importantly the substrate-primer interface.
Apart from enabling selective removal of the coating layer, the selectively strippable coating system must also conform to the application and in-service performance requirements necessitated by the application. In terms of aerospace coating systems, these include the required chemical resistance (for example, to hydraulic fluids and to aviation fuels and cleaners), environmental durability, mechanical properties, aesthetics (colour and gloss), and adhesion.
There may be deficiencies in using the intermediate and barrier coating techniques described above. These may include tight application window tolerances, reduced in-service performance, decreased selectivity or impact to the properties of the coating system following repeated stripping and recoating. Another draw back of these techniques is that the intermediate coating or barrier layer may have a thickness of up to 12 microns which can add extra weight. As such there is a pressing need to develop robust strategies which enable coating layers to be selectively removed that themselves, add minimal weight to the overall coating system, and, hence, in the case of aircraft, assist in reducing the operational environmental foot print.